Audio-visual warning system

ABSTRACT

Upon closure of a single, manually operable switch, such as a vehicle horn button, an electrical power source is connected to both an audible and a visual warning element. Timing means are disclosed in a variety of embodiments which insure continued operation of the visual element for a certain time period after closure of the switch whether or not it is opened prior to expiration of such period. In some embodiments, the timing means is effective to delay deactivation of the visual element for a fixed time after opening of the aforementioned switch irrespective of the time for which it is closed, while in other embodiments the visual element is deactivated immediately upon opening of the switch if it has remained closed for more than the predetermined time period. In another disclosed embodiment, a second visual warning element is provided which is constantly activated during operation of a vehicle on which the warning system is utilized.

Umted States Patent 11 1 1111 3,891,986 Lipe et a1. 1 1 June 24, 1975 1 AUDIO-VISUAL WARNING SYSTEM [76] Inventors: Gordon C. Lipe, Box 1 14, Teton Primary P Yusko Village 83025; wimam s. ASSISILZHI ExammerW1ll1am M. Wanmsky Abbe 2O Lakeview Cir Attorney, Agent, or Firm-Charles S. McGulre a Skaneateles, NY 13152 221 Filed; Jan. 14, 1974 [57] ABSTRACT Upon closure of a single, manually operable switch [2]] Appl 4331l6 such as a vehicle horn button, an electrical power Related U.S. Application Data source is connected to both an audible and a visual [63] Continuation-in-part of Ser. No. 204,125, Dec. 12 element Timing l are disclosed in a 1971 P N 3 7 ,49 r1ety of embodiments which msure continued operation of the visual element for a certain time period [52] US. Cl, 340/371; 340/75; 340/326 after closure of the switch whether or not it is opened [51] Im, Cl, G081; 7/00 prior to expiration of such period. In some embodi- [58] Field of Search 340/75, 76, 88, 371, 326 ments. the timing means is effective to delay deactiva- 340/327; 337/83 tion of the visual element for a fixed time after opening of the aforementioned switch irrespective of the [56] Ref e Cited time for which it is closed, while in other embodi- UNITED STATES PATENTS ments the visual element is deactivated immediately upon opening of the switch if it has remained closed 922 for more than the predetermined time period In an- E 2,1956 jrij 340/75 other disclosed embodiment, a second visual warning 2:912:685 11/1959 Thomas 340/326 X element is provided which is constantly activated dur- 1436.728 4/1969 Silverwood et a]. 340 75 g Operation f a hi le n which the warning sys- 3 559 165 1/1971 Kleemann 340/76 X tem is utilized. 3.648.273 3/1972 Gardner A 337/88 X 3,767,966 10 1973 Bell 340/76 x 15 Clams, 13 Drawing Figures 3O 52 g 5p 7 )5 34 PATENTED M 2 4 m5 30 2O g 5\O "bk-OL- 42 SHEET PATENTEI] JUN 24 I975 I l I I I l I I I I I I SHEET PATENTEB JUN 24 I975 F/G. l3

AUDIO-VISUAL WARNING SYSTEM REFERENCE TO RELATED APPLICATION This is a continuation-in-part of copending application Ser. No. 204,125, filed Dec. 12, l97l of the same inventors, now US. Pat. No. 3,786,498.

BACKGROUND OF THE INVENTION This application relates to combined audible and visual warning systems particularly useful on mechanized vehicles and, more specifically, to various means for causing the visible warning element to remain operative for a predetermined time period after the audible element is rendered inoperative.

Vehicles for transporting individuals and materials, including most notably the automobile, are commonly equipped with audible devices, such as horns, and visible devices, such as flashing lights, for signaling their presence and possible impending danger to other vehicular traffic and pedestrians. However, in the most widely used commercial vehicular warning systems there is no cooperative relationship between the audible and visual elements, each requiring separate manual actuation. Thus, only the audible element is normally used as a warning device in a moving vehicle, the flashing lights being used only to indicate such things as the drivers intent to turn or a stalled vehicle.

With automobiles being built with greater interior sound insulation, coupled with the increasing use of radios and tape players, audible warning devices are losing their effectiveness. Not only horns, but also sirens often go unnoticed even by nearby motorists.

It has been previously proposed as an improvement in vehicular warning systems to operate both audible and visible warning devices with a single actuating switch. For example, depression of the horn button may actuate a circuit which not only sounds the born, but also causes a light to flash. The light may serve to attract the attention of others who have not heard the horn, as well as to more readily identify a particular vehicle, the warning system of which has been activated.

As pointed out in the earlier referenced co-pending application, it has been found advantageous to cause the visible element to remain activated for a time after the audible element is deactivated. This quickly attracts attention to the vehicle by a person who may initially be looking in another direction and turns toward the vehicle only after the operator has released the activating switch. In any event, visually identifying the vehicle in question in the shortest possible time is of utmost importance in avoiding collision or injury, and in this respect the continued operation of the visual warning element offers a significant advantage.

SUMMARY OF THE INVENTION The present invention has as a principal object the provision of novel warning devices having both audible and visual elements activated by a single, manually operable switch, or the like, in combination with a number of different means for causing the visible element to remain operative for a predetermined time after the actuating switch has been released. In each embodiment, the visual warning element and means for extending operation thereof beyond the operators release of the actuating switch are shown in combination with typical vehicle horn switch circuitry. Included among the disclosed embodiments are those having switches operated by thermal delay relays, bimetallic elements, air bellows, and centrifugal force.

Also disclosed is a new type of relay for providing delayed deactivation of the visual warning element. The relay has two separate windings with a common core. One winding is of higher resistance and is connected in parallel with an RC timing circuit. This winding operates the visual warning element contacts, while the low resistance winding operates the horn contacts.

The present invention further provides means for attracting attention to the presence of a vehicle independently of operator actuation of a warning device or system. Such means are disclosed in the form ofa running light operated from the vehicle ignition switch circuitry and may conveniently comprise a second filament in a bulb having a first filament, with or without a flasher, operated as part of an audible-visual warning system as described above.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a simplified block diagram of a vehicular warning system illustrating the most basic aspects of the invention;

FIG. 2 is an electrical schematic diagram of conventional motor vehicle horn switch circuitry;

FIG. 3 is a schematic diagram of circuitry embodying the system of FIG. 1;

FIG. 4 is another schematic diagram of such circuitry, showing a novel relay means for operating contacts of the audible and visual warning elements;

FIG. 5 is a block diagram of another form of the invention;

FIG. 6 is a schematic diagram of circuitry embodying the system shown in FIG. 5; and

FIGS. 7-13 are further schematic diagrams of various modifications of the circuitry, and elements operatively associated therewith.

DETAILED DESCRIPTION The block diagram of FIG. I shows an electrical power source 20, such as a battery, connected on one side to horn switch circuitry 22 and additional circuitry designated visual warning system sub-assembly 24. Circuitry 22 is connected to audible warning element 26 and sub-assembly 24 is connected to visual warning element 28, the other side of power source 20 also being connected to each of the warning elements. Manual closure of the vehicle horn switch, normally accomplished by depressing a button on the steering wheel or column, activates horn switch circuitry 22, thereby connecting power source 20 to audible warning element 26 and sub-assembly 24. The latter serves to activate visual warning element 28 and, as later described, to delay deactivation thereof for an appreciable time after the operator has released the horn button, thereby causing horn switch circuitry 22 to disconnect power source 20 from audible warning element 26.

A typical example of horn switch circuitry of the type depicted by block 22 is shown in greater detail in FIG. 2. Power source 20 is schematically indicated as a battery, the same reference numeral being used as in the block diagram, it being understood, of course, that a generator or alternator would normally be electrically coupled thereto in the usual manner. The elements enclosed in dotted lines are those referred to in the block diagram as horn switch circuitry 22. Switch closure element 30 is biased to the open position shown and rep resents the "horn button normally associated with the steering wheel of the vehicle. Manual depression of the horn button closes the circuit providing power to the coil of relay 32, thereby closing relay contacts 34 and connecting the positive side of battery with diode 36. In subsequent schematic illustrations, only the relay contacts are shown for simplicity, it being understood that circuitry such as that shown in FIG. 2, or equivalent, would normally be provided in a complete system.

Turning now to FIG. 3, it may be seen that closure of relay contacts 22 connects battery 20 directly to audi' ble warning element 26, schematically shown as horn 40, and to diode 36 which is included in visual warning system sub-assembly 24. The sub-assembly further includes a relay having coil 42 and core 44, and an RC timing network having resistor 46 and capacitor 48 connected in parallel with coil 42. Upon closure of relay contacts 22, current flow through diode 36 energizes coil 42 to close the normally open relay contacts 50 and charges capacitor 48. Battery 20 is connected through relay contacts 50 to visual warning element 28 which, as illustrated in FIG. 3, comprises lamp bulb 52 and flasher 54. Thus, upon depression of the horn button relay contacts 22 are closed, thereby substantially instantaneously actuating both horn 40 and lamp 52. When the horn button is released, contacts 22 open, thereby disconnecting audible warning element 26 from the power source. However, the charge on capacitor 48 is sufficient to keep coil 42 energized, thus holding contacts 50 closed and keeping visual warning element 28 in an actuated condition. When contacts 22 open, capacitor 48 begins to discharge, eventually reaching a level insufficient to maintain coil 42 in an energized state, thereby allowing contacts 50 to open and disconnect visual warning element 28 from battery 20. The time between opening of contacts 22 and contacts 50 is termed the after-effect" time of the visual warning element and may be fixed at any desired value, within practical limits, by selection of the values of the various components, particularly those of subassembly 24, according to well known techniques. Fuse 56 may be provided, if desired, for protection from overload.

The foregoing portion of the detailed description corresponds essentially to matter disclosed in the referenced co-pending application and is repeated here to clarify the ensuing descriptions of various other embodiments. In the system of FIG. 4, the horn relay is modified in a unique manner to provide operation in the manner described in connection with FIG. 3.

Horn button 30 is arranged, as in FIG. 2, to connect battery 20 across coil 32, thereby closing contacts 34 of the horn relay. The positive side of battery 20 is connected through contacts 34 to both horn 40 and diode 36. Current flow through diode 36 serves to energize coil 42 and to charge capacitor 48 which, in association with resistor 46, forms the earlier described timing network. It will be noted that coils 32 and 42 are associated with a common relay core 58 and that contacts 34 and 50 are both operated thereby.

The action of the relay, and associated circuitry results from the biasing forces tending to hold the two contacts in the open position, and the opposing forces provided by the two relay coils. These forces are such that energization of coil 32 exerts a force strong enough to close both sets of contacts, thereby actuating both horn 40 and lamp 52 upon manual closure of horn button 30. When the horn button opens, coil 32 is immediately deenergized. Coil 42, however, remains encrgized for the time required for capacitor 48 to dis charge. The biasing force exerted by the relay when only coil 42 is energized is sufficient to hold contacts 50 closed, but insufficient to hold contacts 34. In other words, the force exerted by the relay when only coil 42 is energized is between the spring forces tending to open the contacts, being less than one and greater than the other. Thus, lamp 52 remains connected across the battery after horn 40 has been disconnected. Upon deenergization of coil 42, after discharge of capacitor 48, contacts 50 open and the visual warning element is deactuated. It should be noted that only the single relay normally used in conventional horn circuitry is required, with an extra winding and contacts. Coil 32 is of relatively low resistance and coil 42 of high resistance, in the configuration shown. Referring now to FIGS. 5 and 6, the visual warning element is modified to include a bulb, or separate filament, which is turned on and off by the ignition switch, in addition to the bulb or filament which is activated by the horn switch circuitry. The power source is again indicated by refer ence numeral 20, horn switch circuitry 22, visual warning system sub-assembly 24 and audible warning element 26 being connected thereto as in the diagram of FIG. 1. Block 60, labeled running lights and visual warning element," is connected directly to one side of power source 20, and to the other side through subassembly 24 and ignition switch circuitry 62.

In FIG. 6, the same timing system is shown in subassembly 24 as in FIG. 3, including diode 36, resistor 46 and capacitor 48 for controlling energization of coil 42. Relay contacts 50 are connected through flashers 54 to filament 64, thereby causing this filament to flash on and off during the time contacts 50 are closed. Filament 66 is connected to power source 20 through ignition switch circuitry 62, thus being on steadily whenever the ignition switch is in the on position. Both filaments are connected to ground and may, of course, be provided in two or more separate bulbs rather than within a common bulb. Horn 40 is connected as before to horn switch circuitry 22. The running light makes the vehicle instantly visible and attracts the visual senses at all times, including the time during which the visual warning filament is actuated, but in the "off" portion of the flashing cycle.

The remaining FIGS. 7-13 show a number of different embodiments of the visual warning system subassembly. Since power source 20, born switch circuitry 22 and audible warning elements 26 are the same in each embodiment as in those previously described, they will not be described again although they are shown in each Figure.

The combined audible-visual warning system of FIG. 7 is somewhat different in principle from those previ ously described in that the controlled time period during which the visual warning element remains activated begins with closure of the horn switch circuitry, rather than opening. The visual warning system sub-assembly 24 includes diode 68, relay coil 70 for closure of contacts 72 and thermal delay device 74, having heater element 76 and normally closed contacts 78.

Upon closure of the contacts of horn switch circuitry 22, both audible and visual warning elements 26 and 28 are immediately connected to power source 20. Also, coil 70 is energized to close contacts 72, thus providing a separate holding circuit for the relay through contacts 72 and normally closed contacts 78 of thermal delay device 74, and providing power to heater element 76. Upon opening of the contacts of circuitry 22 when the operator releases the horn button, contacts 72 remain closed and visual warning element 28 remains activated for as long as contacts 78 remain closed. When sufficient heat has been generated by element 76, the circuit to both coil 70 and visual warning element 28 is broken by the opening of contacts 78. The time required to generate such heat is, of course, a function of the design of device 74 and may be established at virtually any desired value by well-known design parameters.

It should be noted that this design, and others to be described later, takes into account the fact that the requirement for extended actuation of the visual warning system diminishes with longer operator actuation of the combined audible and visual warning system. That is, if the horn is sounded continually for a period of, say, 6 seconds or longer, in conjunction with the flashing of a light, it may be assumed that sufficient warning has been given. In systems such as that of FIG. 7, if the horn switch circuitry is kept closed for a time period longer than that required for element 76 to cause contacts 78 to open, then both the audible and visual warning elements will be deactivated as soon as the horn button is released. Thus, in the great majority of cases where the horn button is depressed for a relatively short time, the light will continue to flash after the horn button is released and the audible warning element deactivated. The duration of the after-effect will depend upon the length of time the horn button is depressed, since heater element 76 receives power from the time the horn switch circuit is closed. In the infrequent instances where the horn button is continually depressed for a time longer than that required for contacts 78 to open, both the audible and visual warning elements will remain activated as long as the horn button remains depressed, and both will be simultaneously deactivated upon release of the horn button.

The visual warning system subassembly 24 of FIG. 8 includes diodes 80 and 82 and thermal delay device 84 having heater element 86 and normally open contacts 88. When the contacts of horn switch circuitry 22 are closed by manual depression of the horn button, both audible and visual warning elements 26 and 28 are immediately connected across power source 20, the latter through diodes 80 and 82. Also, heater element 86 is activated and, when sufficient heat has been generated, causes contacts 88 to close. Thus, after the horn button is released, bulb 52 and flasher 54 remain connected to power source through contacts 88 until they cool sufficiently to return to their normally open position. This will depend on the length of time for which the horn switch contacts are closed to connect heater element 86 with power source 20, and on the design parameters of device 84.

In FIG. 9 is disclosed a further modification operable in the manner of the FIG. 7 system. Visual warning system subassembly 24 includes diode 90, relay coil 92 which when energized closes contacts 94, and device 96 having bi-metallic strip 98 surrounded by heater coil I00 and stationary contact 102. When the contacts of horn switch circuitry 22 are closed, both audible and visual warning elements are immediately actuated, the latter via line 104. In addition, coil 92 is energized,

closing contacts 94, and coil 100 receives power via line I06 to begin heating bi-metallic strip 98. When the contacts of circuitry 22 open in response to release of the horn button, coil 92 remains energized due to the secondary holding circuit through strip 98, contact I02 and contacts 94, back to coil 92. Visual warning element 28 will also remain activated, receiving power through the same circuit, until sufficient heat has been generated by coil 100 to cause bi metallic strip 98 to move away from stationary contact 102, thereby breaking the circuit to both the visual warning element and coil 92 of the mechanical relay. As previously described in connection with FIG. 7, if the horn button is depressed for a sufficiently long period, both the audible and visual warning elements will be immediately dc activated upon its release.

Referring now to FIG. 10, visual warning subassembly 24 includes diode 108 and oil-can switching device 110 having heater element 112, oil-can disc 114, insulator 116 and contacts 118. When the contacts of horn switch circuitry 22 are closed, both the audible and visual warning elements are immediately activated, the latter via line I20. Also, heater element 112 receives power and is thereby expanded to move disc 114 and insulator [I6 attached thereto upwardly, as shown in FIG. 10. This moves the lower of contacts 118 into engagement with the upper contact, whereby power source 20 is still connected to visual warning element 28 after the horn switch contacts open. The light continues to flash until heater element 112 has cooled sufficiently after its connection to the power source is broken by releasing the horn button, thereby returning disc 114 to its original position and opening contacts 118.

FIG. 11 illustrates how the originally described embodiment, that of FIG. 3, may be operated from the negative side of the battery. In this configuration, electrical connections are made within the horn switch circuitry, i.e., between the horn button and horn relay coil rather than merely from the output of the horn switch circuitry as in previous embodiments. In FIG. 11 the battery of power source 20 is shown with the ground or negative side uppermost, as opposed to its orientation in all other figures. The same reference numerals are used in FIG. II as in FIGS. 2 and 3 since all of the same elements are present. Horn button 30 is closed to connect coil 32 of the horn relay to ground, thereby energizing the coil and closing contacts 34 of the horn relay. This connects horn 40 to the positive side of the battery. Closure of horn button 30 also energizes coil 42 of visual warning element subassembly 24 and allows capacitor 48 to charge by connecting both of these elements to the negative side of the battery. Closure of contacts 50 activates visual warning element 28, connecting this element to the positive side of the battery. When horn button 30 is released, coil 32 is immediately de-energized, contacts 34 open, and power to horn 40 is removed. Capacitor 48 discharges through coil 42, maintaining contacts 50 closed and providing power to visual warning element 28 until the charge is dissipated. Thus, the same effect is achieved as in the FIG. 3 embodiment, but with opposite polarity. It will be noted that, if desired, each of the embodiments described in connection with the other Figures may be connected to operate in this manner.

FIGS. 12 and 13 show how mechanical elements may be used in practising the invention. In FIG. 12, closure of horn switch circuitry 22 energizes solenoid coil [22, through diode 123 and actuates both audible and visual warning elements 26 and 28. Armature 124 of the solenoid is thus moved to compress bellows 126 which is biased to a normally extended position by spring 128. Contacts I30 are brought into sliding engagement when the bellows is compressed, thus connecting the visual warning element to the battery after the horn button is released. The rate ofexpansion of bellows 126 is governed by the size of opening 132 and the strength of spring 128. This determines the length of time required for contacts 130 to open and deactivate visual warning element 28.

Closure of horn switch circuitry 22 in the FIG. 13 embodiment provides power immediately to audible warning element 26 and through diode 135 to motor 136. Power is also provided to charge capacitor 138 of an RC timing network connected in parallel with the motor windings and including resistor 140. The motor shaft carries flywheel 142 having contact 144 pivotally mounted in a recess in the periphery thereof. Contact 144 is connected via line 146 to the positive side of the battery. As motor [36 turns flywheel 142, centrifugal force moves contact 144 about its pivotal mounting to extend beyond the periphery of the flywheel and touch contact 148 with each revolution. Thus. bulb 52 will flash on and off as long as the flywheel continues to rotate. When the horn button is released, capacitor 138 discharges through the motor windings, thereby causing bulb 52 to continue flashing for the time constant of the RC network. Various possibilities for design modifications exist. including the elimination of the RC network and allowing the inertia of the flywheel to produce the after-effect when power is removed from the motor. Also. a flexible contact may be attached directly to the flywheel or motor shaft. but the pivotally mounted contact shown, or mechanical equivalents thereof, insures that contacts 144 and 148 cannot remain in contact when the motor comes to a stop.

Although the present disclosure, for purposes of uniformity, has consistently referred to relays of the conventional electro-mechanical type. it will be understood that solid state devices with similar function may be substituted therefor.

What is claimed is:

l. A combined audible-visual warning system for use with a vehicle, or the like, comprising:

a. an electrical power source;

an electrically operated audible warning element; an electrically operated visual warning element; a single, manually operable switch selectively closable to effect connection of both said audible and visual warning elements to said power source; and e. timing means effective to insure that electrical power is provided to said visual warning element for at least a predetermined minimum time after closure of said switch irrespective of whether said switch is retained in the closed position for such minimum time, said timing means comprising a relay having:

i. a first coil energized by closure of said switch;

ii. first contacts closed by energization of said first coil to connect said audible warning element to said power source;

iii. second contacts closed by energization of said first coil to connect said visual warning element to said power source;

iv. a second coil energized by closure of at least one of said switch and said first contacts. and an RC timing network connected in parallel with said second coil to maintain the latter in an energized condition for a predetermined time after said first coil is deenergized by opening of said switch, the force exerted by said relay when said first coil is deenergized and said second coil is energized being effective to maintain only said second contacts closed.

2. The invention according to claim 1 and further including a second switch and a second visual warning element activated by closure of said second switch. and wherein operation of the vehicle with which the warning system is associated necessitates closure of said second switch.

3. The invention according to claim 2 and further including an electrical ignition system associated with the vehicle. and wherein closure of said second switch connects said ignition system to said power source.

4. The invention according to claim 1 wherein said timing means comprises a thermal delay device.

5. The invention according to claim 4 wherein said thermal delay device includes a heater element connected to said power source by closure of said switch and a pair of normally closed contacts opened a predetermined time after connection of said heater element to said power source, and said timing means further comprises a relay having a coil energized by closure of said switch to close the relay contacts, and a circuit connection from said power source to both said relay coil and said visual warning element through said relay contacts and said normally closed contacts, whereby said coil remains energized and said visual warning element remains activated for at least the time required for said heater element to cause said normally closed contacts to open.

6. The invention according to claim 4 wherein said thermal delay device includes a heater element connected to said power source by closure of said switch and a pair of normally open contacts which closed in response to connection of said heater element to said power source and open a predetermined time after disconnection of said heater element from said power source, a first circuit connection from said power source through said switch to said visual warning element, and a second circuit connection from said power source through said normally open contacts to said visual warning element, whereby the latter remains connected to said power source for said predetermined time after said switch opens.

7. The invention according to claim 4 wherein said thermal delay device comprises a bi-metallic device.

8. The invention according to claim 4 wherein said thermal delay device comprises an oil-can type switch.

9. The invention according to claim 8 wherein said oil-can switch includes a heater element and a pair of normally open contacts.

10. The invention according to claim 1 wherein said timing means comprises a retractable and expansible bellows.

H. The invention according to claim 10 and further including a pair of contacts moved between closed and open positions by retraction and expansion of said bellows. spring means biasing said bellows toward the position wherein said contacts are open, and means for moving said bellows to the position wherein said power source being connected to said visual warning element only when said contacts are in the closed position.

14. The invention according to claim 13 and further including means for maintaining said motor in an energized condition for a predetermined time after said switch is opened.

15. The invention according to claim 14 wherein said means for maintaining said motor in an energized condition comprises an RC timing network. 

1. A combined audible-visual warning system for use with a vehicle, or the like, comprising: a. an electrical power source; b. an electrically operated audible warning element; c. an electrically operated visual warning element; d. a single, manually operable switch selectively closable to effect connection of both said audible and visual warning elements to said power source; and e. timing means effective to insure that electrical power is provided to said visual warning element for at least a predetermined minimum time after closure of said switch irrespective of whether said switch is retained in the closed position for such minimum time, said timing means comprising a relay having: i. a first coil energized by closure of said switch; ii. first contacts closed by energization of said first coil to connect said audible warning element to said power source; iii. second contacts closed by energization of said first coil to connect said visual warning element to said power source; iv. a second coil energized by closure of at least one of said switch and said first contacts; and an RC timing network connected in parallel with said second coil to maintain the latter in an energized condition for a predetermined time after said first coil is deenergized by opening of said switch, the force exerted by said relay when said first coil is deenergized and said second coil is energized being effective to maintain only said second contacts closed.
 2. The invention according to claim 1 and further including a second switch and a second visual warning element activated by closure of said second switch, and wherein operation of the vehicle with which the warning system is associated necessitates closure of said second switch.
 3. The invention according to claim 2 and further including an electrical ignition system associated with the vehicle, and wherein closure of said second switch connects said ignition system to said power source.
 4. The invention according to claim 1 wherein said timing means comprises a thermal delay device.
 5. The invention according to claim 4 wherein said thermal delay device includes a heater element connected to said power source by closure of said switch and a pair of normally closed contacts opened a predetermined time after connection of said heater element to said power source, and said timing means further comprises a relay having a coil energized by closure of said switch to close the relay contacts, and a circuit connection from said power source to both said relay coil and said visual warning element through said relay contacts and said normally closed contacts, whereby said coil remains energized and said visual warning element remains activated for at least the time required for said heater element to cause said normally closed contacts to open.
 6. The invention according to claim 4 wherein said thermal delay device includes a heater element connected to said power source by closure of said switch and a pair of normally open contacts which closed in response to connection of said heater element to said power source and open a predeTermined time after disconnection of said heater element from said power source, a first circuit connection from said power source through said switch to said visual warning element, and a second circuit connection from said power source through said normally open contacts to said visual warning element, whereby the latter remains connected to said power source for said predetermined time after said switch opens.
 7. The invention according to claim 4 wherein said thermal delay device comprises a bi-metallic device.
 8. The invention according to claim 4 wherein said thermal delay device comprises an oil-can type switch.
 9. The invention according to claim 8 wherein said oil-can switch includes a heater element and a pair of normally open contacts.
 10. The invention according to claim 1 wherein said timing means comprises a retractable and expansible bellows.
 11. The invention according to claim 10 and further including a pair of contacts moved between closed and open positions by retraction and expansion of said bellows, spring means biasing said bellows toward the position wherein said contacts are open, and means for moving said bellows to the position wherein said contacts are closed in response to closure of said switch, said power source being connected to said visual warning element only when said contacts are in the closed position.
 12. The invention according to claim 11 wherein said means for moving said bellows comprises a solenoid.
 13. The invention according to claim 1 wherein said timing means comprises an electric motor initially energized in response to closure of said switch, and a pair of normally open contacts movable to the closed position in response to energization of said motor, said power source being connected to said visual warning element only when said contacts are in the closed position.
 14. The invention according to claim 13 and further including means for maintaining said motor in an energized condition for a predetermined time after said switch is opened.
 15. The invention according to claim 14 wherein said means for maintaining said motor in an energized condition comprises an RC timing network. 